Methods of manufacturing glass substrate for minimizing platinum inclusions and devices using the methods

Abstract

This invention provides a method for manufacturing a glass substrate with minimized platinum inclusions. The method involves processing molten glass using a processing apparatus, at least a portion of which comprises a platinum group metal material. The method includes the following steps: heating the glass material in a furnace to form molten glass; supplying the processing apparatus with a high-temperature zone and a low-temperature zone; controlling the temperature difference in the high-temperature zone to below 30°C, reducing the oxygen partial pressure in the high-temperature zone, and / or increasing the oxygen partial pressure in the low-temperature zone; and supplying the processed molten glass to a forming apparatus to form a glass substrate. This invention also provides an apparatus for manufacturing a glass substrate with minimized platinum inclusions.

Description

[Technical Field]

[0001] This invention relates to a method and apparatus for minimizing platinum inclusions in a glass manufacturing process using a platinum structure. [Previous Technology]

[0002] Liquid crystal displays (LCDs) are representative of flat panel display devices that use rectangular thin-plate glass substrates. In the manufacture of such substrate glass, the overflow-pull method, which horizontally overflows molten glass, is widely used due to the excellent flatness and surface properties of the substrate glass. Components or containers in the manufacturing apparatus that come into contact with the molten glass are typically made of platinum group metals or platinum group metal alloys, or coated with platinum group metals or platinum group metal alloys.

[0003] Platinum, as one of the platinum group elements, is a thermodynamically heat-resistant metal that does not oxidize in air even at temperatures far above its melting point of 1,769°C, and it does not oxidize even at its boiling point of 4,170°C. Furthermore, platinum exhibits low chemical reactivity, low glass contamination, low glass wettability, excellent shape workability, and can be used as a resistor in DC heating systems. Therefore, it is frequently used as a material for containers or transport paths of molten glass during the manufacturing process of glass substrates.

[0004] However, when platinum comes into contact with molten glass at high temperatures (typically above 1600°C in the manufacture of LCD substrate glass), it reacts with oxygen physically dissolved in the molten glass and then dissolves into the molten glass as an oxide. The reaction between platinum and the physically dissolved oxygen in the molten glass is also related to the glass composition. More specifically, phosphate glasses with low melting points, such as laser glasses, exhibit platinum oxidation and dissolution into the molten glass at relatively low temperatures.

[0005] In technical document 1, as shown in Equation 1, it is reported that platinum reacts with oxygen physically dissolved in molten glass, is oxidized and dissolved into the molten glass. Pt 0(s) + n / 4•O2(glass) ⇌ Pt n+(glass) + n / 2•O 2-(1) K Pt(T) = [Pt n+(glass)]•[O 2-] n / 2 / [Pt(s)]•aO 2 n / 4(2) K' Pt(T) = K Pt(T)•[Pt(s)] / [O 2-] n / 2= [Pt n+(glass)] / aO 2 n / 4(3) log[Pt n+(glass)] = n / 4•log aO 2+ log K' Pt(4) (s: solid, a: active, K: equilibrium constant, O 2: physically dissolved oxygen)

[0006] The solubility of platinum in glass, derived from the equilibrium constant K in Equation 2, is given by Equations 4 to 3. Furthermore, the solubility of platinum increases with increasing oxygen activity and is proportional to n / 4 of the oxidation state (n) of platinum present in the molten glass, as shown in Equation 4. Although we know that the reaction between platinum and oxygen depends on the oxygen activity in the molten glass, as shown in Equations 1 and 2, the thermodynamic free energy of platinum remains unknown; therefore, the temperature at which the reaction occurs can only be determined empirically.

[0007] Oxygen dissolved in molten glass can be generated by the decomposition of tin dioxide and the decomposition of water and sulfate.

[0008] In another patent document, KR 10-1135919, an electromotive force is disclosed during the manufacturing process of a glass substrate due to the contact between platinum group elements or platinum group element alloys and molten glass. Therefore, a method is provided to prevent platinum dissolution by externally applying a potential to at least a portion of the manufacturing process to counteract the electromotive force. Although many anti-bubble technologies have been developed by relevant glass companies, countermeasures targeting the principles of platinum inclusion formation are few.

[0009] In fact, when platinum reacts with oxygen physically dissolved in molten glass and is oxidized and contained in the molten glass in an ionic state, it is not yet a defect. However, due to changes in conditions such as temperature and oxygen partial pressure in the molten glass, the dissolved platinum oxide is reduced to platinum metal and precipitates, making platinum a defect, known as platinum inclusions. If platinum inclusions exist near the surface of the glass substrate, they are likely to appear as protrusions on the glass substrate. Protrusions on the surface of the glass substrate can cause pattern breaks or short circuits during the LCD film formation process, which can lead to display defects. Currently, the glass substrate industry has no clear solution for controlling platinum inclusions.

[0010] [Patent Document] (Patent Document 01) Korean Patent No. 10-1135919 [Technical Document] (Technical Document 01) M. Yamamoto and R. Akiyama, Reports Res. Lab. Asahi Glass Co., Ltd., 56, 7 (2006) [Summary of the Invention]

[0011] It can be seen that there are two effective ways to reduce platinum inclusion defects. The first way is to reduce the amount of oxygen physically dissolved in the molten glass in the high-temperature zone, thereby minimizing the amount of platinum dissolved in the molten glass in an ionic state and thus inhibiting the oxidation of platinum.

[0012] The second approach is to minimize the reduction of platinum by increasing the amount of physically dissolved oxygen in the low-temperature zone, so that platinum dissolved in the molten glass in an ionic state can remain in an ionic state and will not precipitate as platinum metal.

[0013] Therefore, the present invention is designed to solve the above-mentioned problems, and the above-mentioned problems are solved by the following configuration.

[0014] It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory, and not intended to limit the invention as claimed.

[0015] The present invention provides a method for manufacturing a glass substrate for minimizing platinum inclusions. The method involves processing molten glass using a processing apparatus, at least a portion of which comprises a platinum group metal material. The method includes the following steps: heating the glass material in a furnace to form molten glass; supplying the molten glass to a processing apparatus having a high-temperature zone and a low-temperature zone; controlling the temperature change in the high-temperature zone and / or applying a potential to the high-temperature zone and / or the low-temperature zone.

[0016] According to the above invention, the temperature change in the high-temperature zone is less than 30°C.

[0017] According to the invention described above, the potential applied in the high-temperature region is positive.

[0018] According to the invention described above, the potential applied in the high-temperature region is a DC potential.

[0019] According to the invention described above, the oxygen partial pressure in the high-temperature zone is reduced due to the applied potential.

[0020] According to the invention described above, the potential applied in the low-temperature region is negative.

[0021] According to the invention described above, the potential applied in the high-temperature region is a DC potential.

[0022] According to the invention described above, the oxygen partial pressure in the low-temperature region increases due to the applied potential.

[0023] According to the above invention, the high-temperature zone includes at least a refining tank, and the temperature difference between the refining tank and the platinum tube connecting the refining tank and the furnace is controlled to be below 30°C.

[0024] According to the above invention, the temperature of the refining tank is above 1620°C.

[0025] According to the above invention, the low temperature zone includes at least a stirring tank.

[0026] According to the above invention, the high temperature zone is above 1575°C.

[0027] According to the above invention, the low temperature zone is below 1400°C.

[0028] According to the invention described above, the forming apparatus forms a glass substrate by using an overflow pull-down method, a floating method, or a slit pull-down method to form a glass substrate.

[0029] The present invention further provides an apparatus for manufacturing a glass substrate to minimize platinum inclusions, comprising: a furnace for heating glass material to form molten glass, a processing apparatus having a high-temperature zone and a low-temperature zone, and a forming apparatus for forming the molten glass into a glass substrate, wherein the high-temperature zone and / or the low-temperature zone are provided with a current control device.

Implementation Method

[0032] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, wherein the same numbers in different drawings denote the same or similar elements unless otherwise stated. The embodiments set forth in the following description of the exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with aspects of the present invention as described in the appended claims.

[0033] In this invention, the terms "positive potential" and "negative potential" are relative terms, indicating that the potential applied to one end is higher than that to the other end. It does not refer to the absolute potential in electrochemistry.

[0034] FIG1 shows and schematically describes an apparatus for manufacturing a glass substrate having the features of the present invention.

[0035] As shown in Figure 1, during the manufacturing process of the glass substrate, molten glass 9 is supplied from furnace 1 to forming apparatus 8 via processing device 7. Processing device 7 includes at least a high-temperature zone and a low-temperature zone. More specifically, the high-temperature zone with a temperature above 1575°C includes a first platinum tube 3 and a refining tank 4. The low-temperature zone with a temperature below 1400°C includes a stirring tank 5 and a second platinum tube 6.

[0036] In the high-temperature zone, the glass is melted in the furnace 1 by a mixture of combustion of the upper gas and direct current heating through the furnace electrode 2. Then, the molten glass 9 is supplied to the refining tank 4 through the first platinum tube 3 to remove air bubbles.

[0037] In the low-temperature zone, after the refining process, the molten glass is homogenized in the stirring tank 5 by the stirrer shaft 15 to reduce the inhomogeneity of the glass composition. Finally, the molten glass 9 is supplied to the forming device 8 through the second platinum tube 6.

[0038] The temperature of each part of the processing device 7 can be adjusted independently. For example, the temperature of the first platinum tube 3 and the refining tank 4 in the high-temperature zone can each be adjusted independently.

[0039] In the forming apparatus 8, the glass substrate can be formed by overflow pull-down method, floating method or slit pull-down method.

[0040] Typically, during the manufacturing process of the substrate glass, when the molten glass 9 in the furnace 1 at a temperature above 1600°C comes into direct contact with platinum (e.g., the first platinum tube 3), the platinum reacts with oxygen physically dissolved in the molten glass 9 in the high-temperature zone, is oxidized, and dissolves in the molten glass 9. Subsequently, when the molten glass comes into contact with platinum at a temperature below 1400°C, the platinum hardly dissolves in the molten glass in the low-temperature zone, but is reduced and precipitated as platinum inclusions.

[0041] To minimize platinum inclusions during glass manufacturing, the present invention provides two approaches. The first approach is to minimize the amount of oxygen physically dissolved in the molten glass in the high-temperature zone, thereby minimizing the ionic dissolution of platinum in the molten glass and inhibiting platinum oxidation. The second approach is to minimize platinum reduction by increasing the amount of oxygen physically dissolved in the low-temperature zone, so that platinum dissolved in the molten glass in the ionic state can remain in the ionic state and will not be reduced and precipitate as platinum metal.

[0042] Regarding the first approach, the present invention provides two methods for reducing the amount of oxygen physically dissolved in molten glass. The first method is to control the temperature change in the high-temperature zone. The mechanism of the first method is summarized as follows.

[0043] The oxygen solubility in molten glass depends on temperature. That is, oxygen solubility increases as the temperature decreases, and decreases as the temperature increases. This means that dissolved oxygen tends to move from high-temperature regions to low-temperature regions. Therefore, it is important to prevent the molten glass from being partially cooled in the high-temperature region.

[0044] In this invention, the furnace 1 is above 1600°C, and the refining tank 4 is maintained at a high temperature above 1620°C to facilitate the decomposition of the refining agent SnO2, thereby removing bubbles. Therefore, the molten glass 9 can be partially cooled while being conveyed through the first platinum tube 3. Therefore, in order to reduce platinum oxidation into the molten glass as it passes through the first platinum tube 3, in this invention, the temperature difference between the first platinum tube 3 connecting the furnace 1 and the refining tank 4 is controlled to be less than 30°C, so that the oxygen solubility near the wall of the first platinum tube 3 does not increase.

[0045] Therefore, by controlling the temperature difference in the high-temperature zone to less than 30°C, the oxygen solubility near the wall of the first platinum tube (3) can be reduced, thereby reducing the amount of platinum dissolved into the molten glass.

[0046] Detailed information on embodiments and comparative examples of the first method of the first approach is shown in Table 1.

[0047] In this invention, the defect level is evaluated by calculating the number of defects in a piece of glass, the number of defects in one kilogram of glass, or the number of good glass pieces per hour. For example, it can be evaluated by calculating the number of defective parts per million glass components.

[0048] [Table 1] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 First Pt tube temperature (°C), (A) 1600 1597 1610 1605 1580 1575 1590 Refining tank temperature (°C), (B) 1625 1620 1620 1623 1620 1621 1623 BA (°C) 25 twenty three 10 18 40 46 33 Pt inclusion defect level ○ ○ ⦾ ⦾ X X X (⦾: excellent, ○: good, X: defective)

[0049] The second method is to apply a potential in the high-temperature region. The mechanism of the second method is summarized as follows.

[0050] Typically, an AC current is applied to heat molten glass. When a direct current (DC) is generated in the molten glass and electrolysis occurs as shown in the following formula, excess oxygen is produced. Therefore, the DC current generated due to various factors such as electrochemical reactions may affect the oxygen partial pressure of the molten glass and may affect the amount of physically dissolved oxygen. For example, if a positive potential is applied to the molten glass and a negative potential is applied to platinum, the alloying reaction of water or SnO as shown in the following formula will be suppressed, and the production of oxygen will also be suppressed. H₂O (melt) + Pt → PtxHy (alloy) + 1 / 2•O₂ SnO (melt) + Pt → PtxSny (alloy) + 1 / 2•O₂

[0051] In this invention, the first platinum tube current control device 12 is located in the high-temperature zone to reduce the oxygen partial pressure. The first platinum tube current control device 12 applies a negative potential to the first platinum tube 3 through the first platinum tube current supply line 11, and applies a positive potential to the furnace probe 10 electrically. The applied potential is a low voltage of less than 1 volt.

[0052] Detailed information on embodiments and comparative examples of the second method of the first approach is shown in Table 2.

[0053] [Table 2] Example 1 Example 5 Comparative Example 3 Example 6 Comparative Example 2 Example 7 First Pt tube temperature (°C), (A) 1600 1600 1590 1590 1575 1575 Refining tank temperature (°C), (B) 1625 1625 1623 1623 1621 1621 BA (°C) 25 25 33 33 46 46 Furnace probe – first Pt tube DC DC DC Pt inclusion defect level ○ ⦾ X ○ X ○ (⦾: excellent, ○: good, X: defective, DC: apply direct current)

[0054] The second approach is to minimize the reduction of platinum by increasing the amount of physically dissolved oxygen in the low-temperature region, so that platinum dissolved in the molten glass in an ionic state can remain in the ionic state without being reduced and precipitating as platinum metal. For this second approach, the present invention provides a method for applying a potential in the low-temperature region to maintain platinum dissolved in the molten glass in an ionic state. The mechanism of this method is summarized as follows.

[0055] It is known that when platinum is oxidized in an ionic state in molten glass, it is not a defect. Therefore, platinum only becomes a defect when the dissolved platinum is reduced to platinum metal and precipitates, for example in the low-temperature region.

[0056] More specifically, after the refining process, molten glass 9 containing SnO formed by the reduction of SnO 2 is supplied to the stirring tank 5. As shown below, SnO can react again with the residual oxygen in the molten glass 9 and be oxidized to SnO 2, wherein large bubbles become smaller, and small bubbles are absorbed and dissipated. SnO + 1 / 2•O 2 → SnO 2

[0057] Simultaneously, in the low-temperature zone below 1400°C, including the stirring tank 5, the second platinum tube 6, and the forming device 8, SnO is the strongest component for reducing PtO x / 2, and platinum precipitates through the reaction shown below: PtO x / 2 + SnO → Pt + (2+x) / 4•SnO 2

[0058] Therefore, increasing the oxygen partial pressure of the molten glass in the low-temperature zone can enhance the oxidation of SnO to SnO2, thereby inhibiting the reduction of PtOx / 2 to platinum metal. To achieve the above objective, in this invention, a potential is supplied between the molten glass 9 and the stirring tank 5 to increase the oxygen partial pressure of the molten glass 9. More specifically, the stirring tank current control device 16 applies a positive potential to the stirring tank current supply line 13 connected to the wall of the stirring tank 5 and applies a negative potential to the stirring tank probe 14. The applied potential is a low voltage of less than 1 volt.

[0059] As a result, the reduction of PtO x / 2 to platinum and the precipitation of platinum can be reduced.

[0060] Detailed information on embodiments and comparative examples of the method is shown in Table 3. [Table 3] Example 1 Example 8 Example 9 Comparative Example 3 Example 10 Example 11 Comparative Example 2 First Pt tube temperature (°C), (A) 1600 1600 1590 1590 1575 1575 1575 Refining tank temperature (°C), (B) 1625 1625 1623 1623 1621 1621 1621 BA (°C) 25 25 33 33 46 46 46 Furnace probe – first Pt tube DC Stirring tank – Stirring tank probe DC DC DC DC Pt inclusion defect level ○ ⦾ ⦾ X ⦾ ⦾ X (⦾: excellent, ○: good, X: defective, DC: apply direct current)

[0061] The above approaches and methods can be combined to minimize platinum inclusions.

[0062] [Industrial Availability] The present invention is suitable as a method for minimizing platinum inclusion defects (which are among the biggest defects in special glass and LCD substrate glass using platinum structures) and can be used to produce glass using platinum structures, such as mobile phone cover glass and ultra-thin flat glass. [Simplified Explanation of the Diagram]

[0030] Reference will now be made to the accompanying drawings, which illustrate exemplary embodiments of the invention disclosed herein. In the drawings:

[0031] FIG1 shows the execution of an apparatus for manufacturing an LCD substrate glass having the features of the present invention, and is described schematically.

Claims

1. A method for manufacturing a glass substrate to minimize platinum inclusions, comprising the following steps: Heating glass materials in a furnace to form molten glass; The molten glass is supplied to a processing apparatus having a high-temperature zone and a low-temperature zone; the temperature change of the high-temperature zone is controlled and a potential is applied to the high-temperature zone and / or the low-temperature zone; wherein when a potential is applied to the high-temperature zone, the potential applied to the molten glass is positive; and when a potential is applied to the low-temperature zone, the potential applied to the molten glass is negative.

2. A method for manufacturing the glass substrate as claimed in claim 1, wherein, The temperature change in the high-temperature zone is less than 30°C.

3. A method for manufacturing the glass substrate as claimed in claim 1, wherein, The potential applied in the high-temperature region is a DC potential.

4. A method for manufacturing the glass substrate as claimed in claim 1, wherein, The oxygen partial pressure in the high-temperature zone decreases due to the applied potential.

5. A method for manufacturing a glass substrate as claimed in claim 1, wherein, The potential applied in the low-temperature region is a DC potential.

6. A method for manufacturing a glass substrate as claimed in claim 1, wherein, The oxygen partial pressure in the low-temperature region increases due to the applied potential.

7. A method for manufacturing the glass substrate as claimed in claim 1, wherein, The high-temperature zone includes at least a refining tank, and the temperature difference between the refining tank and the platinum tube connecting the refining tank and the furnace is controlled to be below 30°C.

8. A method for manufacturing a glass substrate as claimed in claim 7, wherein, The temperature of the refining tank is above 1620℃.

9. A method for manufacturing the glass substrate as claimed in claim 1, wherein, The low-temperature zone includes at least a stirring tank.

10. A method for manufacturing a glass substrate as claimed in claim 1, wherein, The high-temperature zone is above 1575℃.

11. A method for manufacturing a glass substrate as claimed in claim 1, wherein, The low-temperature zone is below 1400℃.

12. A method for manufacturing a glass substrate as claimed in claim 1, wherein, The forming apparatus forms a glass substrate by using an overflow pull-down method, a floating method, or a slit pull-down method to form a glass substrate.

13. An apparatus for manufacturing a glass substrate to minimize platinum inclusions, comprising: A furnace for heating glass material to form molten glass, a processing apparatus having a high-temperature zone and a low-temperature zone, and a forming apparatus for forming the molten glass into a glass substrate, wherein the high-temperature zone and / or the low-temperature zone are provided with a current control device, wherein the current control device is configured such that when a potential is applied to the high-temperature zone, the potential applied to the molten glass is positive, and when a potential is applied to the low-temperature zone, the potential applied to the molten glass is negative.

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